Remove attachment host string replace

This host is no longer hard coded anywhere.

// FREEBIE

Gruntfile.js

@@ -126,9 +126,7 @@ module.exports = function(grunt) {
             if (srcpath.match('libtextsecure') || srcpath.match('background.js')) {
               return content.replace(
                 /textsecure-service-staging.whispersystems.org/g,
-                'textsecure-service-ca.whispersystems.org:4433').replace(
-                /whispersystems-textsecure-attachments-staging.s3.amazonaws.com/g,
-                'whispersystems-textsecure-attachments.s3.amazonaws.com');
+                'textsecure-service-ca.whispersystems.org:4433');
             } else {
               return content;
             }